The present invention generally relates to a deformable IOL haptic system. More specifically, the present invention relates to an IOL incorporating a high modulus shaped skeletal frame assembled with low modulus soft hinged zones.
The history of intraocular lenses (IOLs) is a long and varied one. Intraocular lenses can be used to treat a wide diversity of eye conditions ranging from cataracts to any type of eyesight correction. In addition, IOLs can be used to replace an irreversibly damaged lens in the eyexe2x80x94aphakic eyes. Alternatively, the lenses can be used in addition to the natural lens to correct the visionxe2x80x94phakic eyes. These lenses can be placed in the anterior or posterior chambers of the eye.
Early IOL researchers were plagued with problems associated with the materials which were obtainable to them at the time (early 1950""s) making the lenses too heavy and too large. Surgery of the eye was in its infancy and therefore there were many problems with the surgical procedures. Since that time the quality, size and weight of the optics as well as microsurgical procedures have dramatically improved.
The earliest IOL""s were placed in the anterior chamber of the eye, this being the easiest chamber to get to. Along with the early problems with the optics and surgical techniques, placement of a lens in the anterior chamber proved difficult because the anterior chamber is narrow (about 1.5 to 2.5 mm).
Because of the narrow chamber, an IOL can easily come in contact with the corneal endothelial layer, in which case the nondividing cells may be damaged. If enough damage occurs there may be scarring to the cornea which affects eyesight and can cause xe2x80x98dark zonesxe2x80x99. In addition, the two areas available for fixation (i.e., mechanical support) of the IOLs in the anterior chamber created new problems. The first location for attachment is the iris. However, with such attachment, and since it is necessary to allow for the rather considerable movement and patency of the iris, obstructions could result in uveitis and glaucoma.
The second location is the angle between the cornea and the iris. Angle supported anterior chamber IOLs took advantage of, the anterior chamber angle to support and fix the IOL in place. By angling the IOL into opposite sides of the anterior chamber, the natural angle was used to keep the IOL from moving. However, early lenses experienced marked problems with endothelial loss due to chafing against the early thick lenses. Later lenses were able to reduce the significance of this problem, but still retained problems associated with placement of the IOL in the chamber angle. The biological properties of that angle make it a very sensitive area. The structures associated with equalizing the internal pressure of the eye are located in that area. Additionally, the tissue in the area is easily irritated arid irritation initiates a growth of fibrous tissue; called synechiae. The IOL fixation must be gentle in order to reduce irritation, but stable enough that it will not be easily moveable. This compromise is difficult to obtain. In addition, although the results were excellent in the short-term, there was a significant problem in the long term with altered night vision, loss of endothelial cell populations and alteration of the anterior uvea. These problems as well as the fact that such anteriorly positioned lenses were uncomfortable to the patient, caused many doctors to abandon anterior chamber IOL""s.
A third location was developed later and involves implanting a contact lens between the iris and the natural lens. These lenses are called ICL""s or implantable contact lenses. However, the ICL""s are suspected of initiating cataracts and glaucoma.
As the development of the IOL""s became more,sophisticated, Ophthalmologists recognized various problems. A typical IOL is composed of an optic, the xe2x80x98lensxe2x80x99 part of the structure, and a mounting mechanism called a haptic. The haptics are the part of the IOL that comes in contact with the eye tissue to hold the lens optic in place. There were essentially two major types of haptics which were developedxe2x80x94fiber and plate haptics. Fiber haptics are slender strands of resilient material which are attached at one end to the optic, and which rest, at their other end, against the eye. Fiber haptics have the advantage of being very light and slender. This would seem to make them ideal by causing less damage to the tissue and additionally being aesthetically pleasing because they are very narrow. The slenderness makes it more difficult for someone looking at the patient to see the IOL through the eye. Plate haptics are formed as a sheet, which has a central opening to support the optic and an outer perimeter which rests against the eye. Because of their size, plate haptics tend to be more easily seen from outside in the patient""s eye and the addition of extra material weight to the IOL and reduced flexibility as compared to fiber haptics leads to poor fixation and consequent migration or dislocation of the IOL. While, fiber haptics have the disadvantage of initiating a process in which the body builds fibrous tissue or synechiae around the fiber haptic which immobilizes the iris, the larger plate haptic very rarely, if ever, causes such a reaction.
The adverse problems associated with the earlier anterior chamber haptic designs encouraged the development of IOL""s for the posterior chamber for the majority of implants.
Accordingly, an intraocular lens (IOL) has been developed. The intraocular lens features an optic and a haptic. The haptic features a pair of relatively more rigid elements formed of relatively higher modulus (harder) materials which are flexibly springy when thin and, which are separated from one another at a discontinuity; and a relatively less rigid element formed of relatively lower modulus (softer) material bridging the discontinuity. In one arrangement, the bridged element allows for the relatively more rigid element to be angled to fit into the anterior chamber angle. In a further arrangement the haptic features four separate relatively more rigid elements. The higher modulus springy material may be selected from polyimide (such as KAPTON), polyetheretherketone, polycarbonate, polymethylpentene, polymethylmethyl methacrylate, polypropylene, polyvinylidene fluoride, polysulfone, and polyether sulfone. Preferably, the higher modulus material is polyphenylsulfone (PPSU). Preferably, the higher modulus material has a modulus of elasticity of about 100,000 to about 500,000 psi, even more preferably about 340,000 psi and has a hardness of about 60 to 95 on the shore D scale, but more specifically a Rockwell R hardness of 120 to 130. The lower modulus rubbery material may be an elastomer selected from silicones, urethane, or hydrophilic acrylics. Preferably, the lower modulus material has a modulus of about 100 to about 1000 psi (unit load at 300% elongation). Preferably, lower modulus material has a hardness of about 15 to 70 on the shore A scale of hardness. Preferably, the lower modulus material is a dispersion such as NUSIL MED 6600, 6605, 6400, or 6820.
In one embodiment, the relatively more rigid elements comprises a frame. The frame forms a haptic which may be formed from a single uniform piece of material. The frame may have a hinge to allow folding of the intraocular lens. In a further embodiment, the frame may have one or more additional haptics. The haptic may contain a slot open on one side to form a hinge which is bendable at the slot. The haptic may alternatively contain a groove to form a hinge which is bendable at the groove.
In one embodiment, the lens and high modulus portions of the haptics may be formed from a single uniform piece of material. The uniform piece of material may be thin and include a thin lens. Alternatively, the uniform piece may be thick (up to about 1 mm thick), but thinner at the haptics, which are preferably less than or equal to about 0.01 inch thick. The haptic may be intentionally broken at the discontinuity. Alternatively, the region of discontinuity may be sculpted down to be so thin that it is flexible. The optic may be a refractive lens, or an interference lens, producing a thin optic. In one embodiment, the haptic is attached to the optic externally. In another embodiment, the lens is attached to the haptic frame using a bridge.
The lower modulus material may partially or completely cover the haptics. In one embodiment, the lower modulus material is extended beyond the tip of the haptic to produce a softer contact point for the eye tissue. The lower modulus material may be applied by first surface treating the higher modulus material and then molding the lower modulus material onto the treated surface. Preferably, the surface treatment is a corona or plasma treatment and additionally a primer. Preferably, the molding is dip molding, cast molding, or injection molding.
The invention is an intraocular lens frame, having two plate haptic elements each including a foot region and a toe region both formed of relatively higher modulus harder material; and a hinge connecting the toe region to the foot region, the hinge being formed of relatively lower modulus material. This can be referred to as a xe2x80x9cduplexxe2x80x9d material.
Further, the invention is an intraocular lens having an optic; and a haptic including a pair of stiffer elements joined by a flexible element of different material.
Still further, the invention is a method for making an intraocular lens haptic, having the steps of forming a frame, coating a location of the frame, and breaking the frame at the location.
Still further, the invention is a method of mounting a lens in the anterior chamber of an eye, having the steps of supporting a lens on a plate haptic at the angle of the anterior chamber; and bending the haptic at a preferential hinge line to reduce pressure against the angle.